The present invention relates generally to a system for use in laser treating material and more particularly to a method and apparatus for rapidly providing half-cuts or score lines or various other laser treatments in material.
Many process systems known today use a continuous web feed of uncut material into a process. For example, in the packaging industry, a continuous web of material is fed through a printing system and later it is cut into individual packaging units to be folded into a desired package configuration. A newspaper printing press is another example of a continuous feed of material (i.e. paper) passing through a printing process, later to be cut into individual sections.
Of course, printing is not the only process that is incorporated into such systems, and paper is not the only kind of material that is continuously fed into such systems. Industry in general has applied many different processes to many different materials in continuous feed systems.
The ability to process on a web of material with a laser system requires that the power, tracking, and optics handle the requirements of full web speed. Conventional web system processes, such as that shown in U.S. Pat. No. 5,001,325, are characterized by high speeds which may require a large field of view in the web direction to allow for tracking and thus resulting in a longer focal length for the laser system. The greater the focal length requirements, the more powerful the laser system must be to process the material.
The present invention provides a process and system wherein shingled sheets of material are passed through a section where a laser system may treat the material. The source of the sheets may be a stack of sheets, or may be a web system sheeter output, or various other discrete material supply techniques. Shingling sheets of material slows the apparent speed of the material through the laser system processing area, relative to the overall web speed, and thus allows a smaller field of view for the laser system to track and perform its function. A higher percentage of overlap allows a slower conveyor speed and lowers the overall system requirements. In addition, in the case where the web repeat length is very large compared to the length required to be processed (i.e., 100 to 1) the amount of time to process can also be increased via shingling in that the field of view need only cover the 1% length while in the web case to have equivalent time to process the entire repeat (100%) need to be tracked. If less than the full repeat is tracked then the process time will be less (i.e., 50% track=1/2 the time available to process). These types of system trade offs significantly affect the power of the laser as well as the scan rates and effective power density at the work surface. Thus it can be seen that this technique allows one to significantly improve the efficiency of using the optimum advantages of the laser and its optical tracking systems.
As a result of the present invention, the power requirements of a laser system may be reduced. With the present invention, the lower power requirements permit the use of laser systems previously thought impracticable for such laser treating systems. Many CO.sub.2 laser systems may now be used along with state of the art galvos systems having finite power handling capabilities.
Shingling allows the conveyor speed to be reduced dramatically. The speed of the shingled blanks riding on a conveyor can be reduced by a factor of 10 if a 90% overlap is used, as compared to the web speed. For example, if a web process running at 200 m/min., supplies a shingling system that has overlap of 90%, the shingling conveyor speed will be 20 m/min. This example assumes that the laser treatment to be performed is to be done on the 10% exposed surface.
Because the speed is reduced to 20 m/min. on the shingling system, it travels 1/10 the distance during the cut cycle. Thus the galvo tracking distance need only be 1/10 of what would be needed on a web system. This in turn allows the use of shorter focal lengths.
The shorter focal length is significant since it is directly proportional to the focused spot diameter. In this example, the galvo focal length is reduced by a factor of 10. This reduction in the spot diameter will have a large impact on the power densities achieved. Since the power density is related to the spot size area, any reduction in the spot diameter will increase power density by the square of the diameter change. The power requirements for the optics can also be decreased accordingly. In addition, the optic path (i.e., galvo, optics, mirrors) need only to carry this lower power requirement.
The present invention may be utilized to provide scores or cut lines in predetermined places in containers to contribute to the consumer-friendliness of a container. Such containers may be easily opened without the use of tools such as scissors or knives.
These and other advantages will be apparent from the following detailed description of the invention, drawings, and claims.